Current hollow core doors have a central lengthwise extending core with a backbone of relatively small cells. These single backbone cores when used in automated door manufacturing have a tendency to curve to one side or the other depending upon variations in the core, the door being assembled and manufacturing inconsistencies. This may cause both performance issues on the automated line and quality issues when the core movement causes the molded panels on one side to have insufficient support, i.e., pillowing.
U.S. Pat. No. 4,583,338 to Sewell, et al., discloses a hollow door panel construction including a rectangular frame of predetermined thickness assembled from side and end members defining an elongated enclosure. Within the enclosure are corrugated paperboard strips, having a width equal to the predetermined thickness. The strips are variously formed and attached to define a plurality of horizontal cell rows, vertically stacked to fill the framed volume. Each cell row spans the internal width of the frame, and includes a centrally positioned short-walled brace cell straddled on either side by a long-walled lateral cell. To complete the panel construction, thin sheets abut and are secured to the opposite faces of the frame and to the outer edges of the strips. In essence, Sewell discloses a single back bone core designed to provide greater door strength. However, as with all single backbone cores, Sewell's single backbone core has a tendency to curve to one side or the other during automated manufacturing depending upon variations in the core. When this curving occurs, the molded panels on one side tend to have insufficient support.
U.S. Pat. No. 2,827,670 to Schwindt discloses a hollow core door wherein the surface sheets have limited relative longitudinal movement with respect to each other and rigid connection of the surface sheets to longitudinally extending stiles is eliminated. Schwindt discloses a single backbone core structure using a higher concentration of cellular material in the vicinity of the edges along the stiles and rails. As with Sewell, the core of Schwindt would have a tendency to curve during manufacture.
There remains a need for a core that provides a more consistent position and coverage in hollow core doors, that resolves both the automated line manufacturing issues such as interference with the hinge blocks and lock blocks, and that resolves quality issues that occur when the door facings have insufficient support from the core.